1. Field of the Invention
The present invention relates to an Internet protocol (IP) multicast communication network handling for example two-way CATV broadcasts etc., more particularly relates to a multicast communication method, multicast transmitting terminal (i.e. source), multicast receiving terminal (i.e. receiver), Layer-2 (L2) switch, and Layer-3 (L3) switch in such a network.
2. Description of the Related Art
At the present time, there are various types of networks able to handle IP multicast communications. Among these, the present invention particularly concerns an IP multicast communication network including at least layer-2 switches using media access control (MAC) addresses, that is, L2 switches.
In such a network, when a multicast receiving terminal forming part of the network issues a request to the effect of desiring distribution of desired video information, the multicast transmitting terminal which transmits the video information distributes the desired video information in response to the request through the network to that receiving terminal.
In this case, the IP multicast packets used for transferring the video information are relayed on the network through the L2 switches. Since they go through the L2 switches, the packets are transferred without identification of the address. Therefore, the network is flooded.
That is, even a network with no multicast receiving terminal under the L2 switches ends up being sent the IP multicast packets without limit. Therefore, wasted traffic occurs and the network resources are not utilized efficiently.
Note that as known art relating to the present invention, there is Japanese Unexamined Patent Publication (Kokai) No. 2000-125277.
Summarizing the problem to be solved by the invention, the IP multicast communication network disclosed in the above publication is basically equivalent to the network of the related art as explained later referring to FIG. 16. According to FIG. 16, an L2 switch is equipped with an Internet group management protocol (IGMP) SNOOPING function. Further, the multicast receiving terminal (receiver) executes an IGMP JOIN operation for layer-3 switches using an IP address, that is, L3 switches such as routers.
However, even with multicast communication using the above IGMP SNOOPING function, there is the problem that this IGMP SNOOPING function cannot be applied to the following two type I and II IP multicast communication networks, that is,
I. A network of a type where the plurality of switches relaying multicast packets between a multicast transmitting terminal (source) and a multicast receiving terminal are all L2 switches and
II. A network of a type where the plurality of switches relaying multicast packets between a multicast transmitting terminal and a multicast receiving terminal are L3 switches, but two adjoining L3 switches have at least one L2 switch interposed between them.